<div id="innerLeft" style="background: #afa">
  <a href="#" id="loadRightPanel">Load right content</a>
</div>
<div id="innerRight" style="background: #aaf">
  
</div>
 <script type="text/javascript" charset="utf-8">
    $('loadRightPanel').addEvent("click",function(ev){
      new Request.HTML({
        update: $('innerRight'),
        evalScripts:true,
        url:'_right_content.html'
      }).get();
      return false;      
    });

  var layout = $('innerLeft').getParent().retrieve("skyline.layout");

  layout.addPanel("innerLeft", {size: "auto"});
  layout.addSplitter("before")
  layout.addPanel("innerRight", {size: "fixed"});  
  
  layout.reinitialize();
</script>